1. Field of the Invention
The present invention relates to a playback method for use in an apparatus for playing a recording medium on which a coded information signal is recorded, such as a digital audio disc, and relates to a recording medium, and a system for recording and reproducing information on and from a recording medium such as a digital audio disc.
2. Description of Background Information
A small size digital audio disc whose diameter is about 12 cm, generally designated as the compact disc, has been known as a recording medium on which a coded information signal is recorded. On the other hand, a disc of a new type (referred to as composite disc hereinafter) has been already developed which has the same size as the compact disc and on which are recorded, in addition to the PCM (pulse code modulation) signal, an FM-modulated video format signal and a PCM signal which are combined together by a frequency multiplex operation.
On the composite disc, information is recorded in its recording area which is separated into a first area located inside in which, for example, audio information is recorded in the form of a PCM signal, and a second area outer than a predetermined diameter, in which the FM-modulated video format signal and the PCM audio signal are recorded after being treated by the multiplexing operation.
As a playback method for use in a disc player for playing a composite disc explained above, a playback method is disclosed in Japanese Patent Application Laid Open No. 61-232645, in which the playback of the first area is performed after the playback of the second area, so that a playback operation can be performed following an order intended by the suppliers of program "softwares" (record materials).
On the other hand, a system is proposed in which picture information is recorded and reproduced in the form of the subcode on and from a digital audio disc. The subcode is made up of eight subcode bits, and bit groups forming the subcode are divided into eight channels denoted respectively by letters P, Q, R, S, T, U, V, and W. In the method in which the picture information is recorded and reproduced in the form of subcode, data corresponding to picture information is configured such that a symbol is formed by 6 bits of channels R through W out of the 8 bits forming the subcode, and 98 symbols are treated as one block, as illustrated in FIG. 1. Two symbols in the 98 symbols are used as a sync signal, and 24 symbols obtained by dividing the remaining 96 symbols, by four are treated as a minimum unit of data, i.e. a "pack", which constitutes one instruction of picture processing.
More specifically, the first symbol (referred to as symbol 0 hereinafter) of the 24 symbols shows one of several modes. A symbol 1 following this symbol 0 forms "instruction" which indicates the sort of the instruction. Symbols 2 and 3 following the symbol 1 constitute a "parity Q" which is an error correction code. Symbols 4 through 19 following the parity Q constitute a data field, and include information such as color information. Finally, symbols 20 through 23 following the data field constitute a parity P which is an error correction code for protecting the information in the "pack".
On the other hand, there are four modes, i.e. "zero mode", "line-graphics mode", "TV-graphics mode", and "user's mode". The "zero mode" is provided for a case where no operation is required for pictures on the display screen, that is, the original image is to be maintained, and all data in the "pack" are 0 for this mode.
The "line-graphics mode" is provided for such a case that a liquid crystal display is provided on the front face of the player, to display notes such as an explanation of a music selection. As shown in FIG. 2, a picture area elongated sideways is formed by pixels which are arranged in 288 columns and 24 rows. In other words, each row includes 288 pixels and each column includes 24 pixels. The term "pixel" stands for the minimum display element of a picture, and it is general that the picture processing is performed by using picture composing units designated as "fonts" each of which is made up of pixels divided into 6 columns and 12 rows.
The number of "fonts" which can be displayed in the "line-graphics mode" is 48 in the lateral direction, and 2 in the column direction, and this area is designated as "screen area". For providing the scroll function, a line of "fonts" is added to the upper and lower outer peripheries and the right and left peripheries of the Screen area, to form a picture area having 50 "fonts" in the direction of row, and 4 "fonts" in the direction of column. The subcode is formed so that the picture processing is performed by using a memory having addresses each corresponding to each pixel in this picture area. In addition, the area outside the "screen area" is designated as "border".
The "TV-graphics mode" is a mode for displaying images on the TV screen, and a picture is formed by pixels arranged in 192 rows and 288 columns as illustrated in FIG. 3. The number of "fonts" which can be displayed in the "TV-graphics mode" is 48 in the direction of row, and 16 in the direction of column. Also in this "TV-graphics mode", the subcode is formed so that the picture processing is performed by using a memory having addresses each of which corresponds to each pixel in a picture area having 50 "fonts" in the direction of row, and 18 "fonts" in the direction of column, made by adding a line of "fonts" to the upper and lower peripheries as well as the right and left outer peripheries of the "screen area".
As instructions for the picture processing, there are an instruction for painting out the whole picture area by one certain color, an instruction for drawing a picture in one "font" on the screen by using two different colors, an instruction for moving the whole picture upward or sideways, and so on.
Additionally, in the 8-bit groups forming the subcode, the Q bits forming the channel Q include time information corresponding to the track length to a certain position of each information data which is recorded from the beginning of the program area of the CD, and form address time data which can be used as positional data representing the recording position. On the other hand, the P bits forming the channel P form data including information relating to a pause between two music selections.
By using the above-described system of recording and reproducing picture information as the subcode, the graphic code including picture information can be recorded as being inserted in the subcode of a digital audio signal to be recorded in the first area of the composite disc. In that case, the program recorded in the first area is likely to be a main program. Therefore, with the conventional playback method in which the reproduction is always started from the second area in the case of the playback of a composite disc, it is feared that the program which is intended to be principal by the supplier of programs is not seen by the viewer on the contrary.